Interference-reducing means for radio receiving apparatus



' 1,616,923 R. H. RANGER INTERFERENCE REDUCING MEANS FOR RADIO RECEIVINGAPPARATUS Filed Dec. 28. 1922 2 Sheets-Sheeizl awuemtoz H RANG ER R. H.RANGER INTERFERENCE REDUCING MEANS FOR RADIO RECEIVING APPARATUS Feb.8,1927. v 1,616,923

Filed Dec. 28. 1 2 Sheets-Sheatz awwentoz R. H- RANGER Patented Feb. 8,1927.

UNITED STATES 1,516,923 PATENT OFFICE.

RICHARD HOWLAND RANGER, OF BROOKLYN, NEW YORK, ASSIGNOR TO RADIO COR-PORATION OF AMERICA, A CORPORATION OF DELAWARE.

INTERFERENCE-REDUCING MEANS FOR RADIO RECEIVING APPARATUS.

Application filed becember 28, 1922. Serial No. 609,375.

This invention relates to means for improving. the reception of signalsthrough interference caused by atmospheric disturbances or so calledstatic or by other transmitting stations having appronimately the samewave length as the desired station. It is an object of this invention toprovide such means which will allow signals from a given station to beselected, distinguishing m sharply over signals from other stations andwhich will at the same time not interfere with the signal desired. It isan object of this invention to provide such means which will berelatively simple and cheap to construct and which shall be reliable andpositive in its action. Other objects Will be apparent from thespecification.

It has been suggested in the past that disturbances might be eliminatedin the reception of signals by thevuse of two receiving antennae,difi'erentiating between received signals as to phase relation; that isto say the signals were received on each antenna and passed on tocircuits which were coupled together in such a way that the desiredsignal was strengthened and the undesired signal was eliminated.

it has also been proposed to apply this scheme to the elimination ofstatic disturbances by providing a plurality of antennae which givecurrents having a definite phase relation, resulting from staticdisturbances and currents having a different phase relation resultingfrom a desired signal. The

1 circuits were then coupled together in such a Way that the staticeffects opposed each other and the signal was strengthened. It has beenfound in practice that under certain conditions this system givessatisfactory protection from interference, but under other conditions isnot entirely satisfactory.

The present invention aims to overcome such interference, as in theformer system, by using two receiving antennae having differentcharacteristics with respect to signals, such as different distance fromthe transmitting station or different directional characteristics,different tuning characteristics, etc. However, instead of providing asin the old system, for a coupling between the two receiving systems insuch a manner that the signals combine, I provide that the signals fromonly one of the'receiving systems reach the detector. The signals fromthe other antenna are used for the purpose til of rendering theindicating means unres sponsive under certain conditions and permittingit to respond under other conditions. It will be pointed out how this isdone in the specification in conjunction with the drawing, and while Ihave shown and described certain arrangements adapted to do this, itwill be understood that my invention is not limited to the meansdisclosed but that modifications and changes may be made as will readilybe understood by those skilled in the art. The scope of my invention,however, will be pointed out in the appended claims.

Referring to the drawing,

Figure 1 is a set of curves explaining the principle of my invention.

Figure 2 is a diagrammatic showing of certain apparatus by the operationof which my invention maybe understood.

Figure 3 is a curve explaining the operation of my invention.

Figures 4, 5, 6, and 7 are various arrangements which may be utilizedaccording to this invention.

It'is well understood that an oscillating circuit having a certainnatural period may be set into oscillation by impulses transferred toit, either through a circuit inductively coupled thereto or by othermeans. The full line curve of Figure 1, group C represents the growth ofan oscillatory current in a circuit, such as shown in Figure 2,comprising inductances 5 and 10 and variable condenser 9, which circuitmay be set into oscillation by the means of coil 5,, connected to somesuitable source. If the frequency of the oscillations in the primarycoil 5 has a value corresponding to the natural frequency of the circuit5 9 10 oscillations will be set up according to the full line curve ofFig. 1, group C. These oscillations will be very weak at first but willincrease in intensity until a steady condition is reached. However, ifby means of key 17 we short circuit condenser 9 periodically for a shorttime at such point on the cycle as shown by Figure 1 that the condenservoltage is maximum. (that is, when the oscillating current is zero) itwill be apparent that no energy can be stored in condenser 9 and thecircuit will not oscillate in spite of the fact that the impulsestransmitted to inductance 5 are in accordance with the natural frequencyof the circuit. This is due to the fact that in order to make such a fora periodical interchange of energy e cycle that ener the condenser, itwill be apparent that no' circuit oscillate it is necessary to provigetween the inductance and capacity, t energy being represented first by acharge upon the condenser and second by a magnetic field linking theinductance.

In the case of a circuit set into oscillations this interchange of enery will continue until the energy is entire y dissipated by losses in thecircuit. 7 j 7 It will be evident, therefore, that H key 17 shown inFigure 2 is closed, any energy which may be resent in the condenser willbe dissipated. Further, if this short circuiting takes place at thebeginning of a series of oscillations, for instance, at the' extremeleft of Fig. 1 very little energy isstored in the condenser by the firstoscillation and very little current will flow during the dischargethereof. If this short circuiting is contmuedperiodically, at such ointon the is tending-to e stored in appreciable amount of energy can everbe stored in the condenser and consequently the oscillating current cannever build up; to all intents and purposes the circuit acts as ifentirely detuned. That is to say, no matter how closely the excitationfollows the natural period of the circuit, the circuit is never set intosteady and pronounced os cillation as shown by full line curve C, but

if it oscillates at all, the oscillations will have only a smallamplitude, such as shown by dotted curve C.

The result of this is therefore the same as if the circuit is entirelydetuned. If, however, this short circuiting takes place at a time whenthe voltage across the condenser is zero and the ener y is. stored .inthe inductances there will i until they reach the maximum amplitude.

This is clearly shown in Fig. 1 in which the curve of group D shown infull lines represents the conductance of the path around the condenserand the dotted line curve re resents the same thing occurring at a. sligtly different time. The corresponding curves of group C then representthe oscillatory currents under these conditions.

This affords a new means of rovidin that certain signal currents will epasse through an oscillatory circuit while others will not be. Forinstance, let it be assumed that instead of operating the key 17providing the condenser short circuit b hand, it is operated under thecontrol 0 a signal from one antenna and that the impulses provided bycoil- 5 are obtained from another antenna. If then the antennae .arelocated with respect to each other in such a way that the signal fromone will cause a short circuiting of'condenser 91 at a point on thecycle where e no effect upon the oscillations which will continue tobuild up the condenser voltage isvsubstantially zero, thesignals'impress'ed upon 5, will build up to a maximum am litude in theoscillating circuit 5 9 10 and y coupling some suitable detector to thiscircuit these oscillations can be detected. However, the oscillationsimpressed upon 5 differing in phase from those which are passed throughwill obviously not be passed on to the detector for the reason that thecondenser will be short circuiteil at some time when the energy isrequired to be stored therein in order to continue oscillations, and asexplained above the circuit will be in effect detuned to the undesiredoscillations. A practical receiving arrange ment utilizing thisprinciple is shown in Figure 4.

B and B respectively designate two'receiving stations having differentcharacteristics, as previously described, provided with the usual tuningmeans, comprising variable inductance 2 and variable capacity 3. Alsophase shifting coils or phase rotators, which are well known in the artand form no part in this invention, may be provided either in the inputor the output of am lifiers 4 and 4 for a pur ose to be explaine later.

The signa.s received upon the antenna of station B are impressed on thecontrol electrodes of a vacuum tube amplifier 4 which has connected inits output circuit the primary 5,, of coupling coil 5. In a similarmanner signals received upon the antenna of station B are impressed on asimilar amplifier 4, having connected in its output circuit the primary6,, of coupling coil 6. The oscillating circuit utilized in thisarrangement consists of the secondary 5 of coupling coil 5, primary 10,,of coupling coil 10, inductance 11 and variable condenser 9. A suitabledetector12 is coupled to the oscillating circuit through secondary 10 ofcoupling coil 10 and any suitable receiving or recording arrangementherein shown as telephone receivers 13 is connected in the outputcircuit of the detector. Two similar three-electrode tubes 7 and 8 arerovided having their plates connected to t e opposite plates ofcondenser 9. The filaments and grids of these tubes are connected as forparallel operation and the secondary 6,

of coupling coil 6- is connected across the con- .trol circuit of thetwo said tubes as shown.

In addition to this, I provide battery 14.- and potentiometer 15 forcontrolling the grid bias of these tubes in a manner to-be explainedlater. 1 It will be apparent from this arrangementthat signals -fromstation actuating station and station B as the controlling station. Theoperation of the arima es rangement is as follows:

If the controlling station is not bein used, it is apparent that bytuning and adjusting the actuating station to the signal desired andtuning the oscillating circuit also to the signal, detector 12 will beset into operation in res onse to the signals which may then be rea edby means of telephone receivers 13. This is entirely suiiicient' forreception where no interference of any sort is experienced, but supposethat interference is being experienced. Thecontrollin'g station willthen be set into operation.

It the antennas of B and B are so situated with respect to one anotherand the transmitt'ing station that the desired signals from theindicating station and from the controlling station are difierentinphase on arrival at the coils 5 and 6. no phase shift ing means arenecessary. lit this is not the case some phase shifting means must beused and arranged so as to give this relation.

The cooperation of the actuating and controlling stations will readilybe understood from the foregoing explanation given for the control ofthe oscillating circuit. @scillations are set up in oscillating circuit5 10 11 9 and condenser 9 is periodically short circuited by one or theother of tubes Y and 8.

lhe periodical short circuiting of condenser 9 coming at the instantwhen the condenser voltage is 0, and maximum current is flowing in theoscillatory circuit, will be without effect on the oscillations takingplace in this circuit and these oscillations will be passed on to thedetector exactly as if the controlling. station were not in-use.Oscillations set up by any disturbance, which are out of phase with thedesired oscillation will not build up in the circuit because thecondenser 9 is short circuited at some point with respect to them whenthey are tending to store energy in the condenserandconsequently willnot. afi'ect'the detector.

Certain precautions must be taken how ever to provide that the systemshall function properly. For instance it is essential that tubes 7 and 8shall respond only to the.

desired signal received at the controlling station, and to no othersignal. This may be achieved by tuning station B assharply as possible,either directionally or to wave length, or by a combination of both.

It is further desirable that the short circuiting of condenser 9 shallbe for an extremely short time and only when the voltage acrosscondenser 9 due to the desired signal is substantially zero. This resultmay be obtained by working tubes '2' and 8 as described in my copendingapplication Serial No. 607,476 filed December 18, 1922, by providing abias on these tubes in such a way that they respond only to the peak ofthe.

signals received at station B. In accordance with the square law theresistance diminishes very greatly when such peak is reached, as shownby Fig. 3 where the dot ted line represents the conductance of tubes 7and 8 and the full line represents the controlling signal. Ordinate arepresents the voltage necessary to be generated by the controllingsignal in order that the conductance of tubes 7 and 8 be altered.

It will be evident that l have provided for short circuiting thecondenser 9 for an extremely short time under the control of the signaldesired to be received and as explained aboveonly the signals whichgives zero voltage of condenser 9 at the time of condenser short circuitwill be impressed upon detector. This provides means for blocking outany static disturbances having a phase relation diderent from thedesired signal but not for blocking out static having the same phase.However. this will occur only relatively infrequently, and the result isthat signals are rendered much more readable.

Modifications of this arrangement may be made, such as shown in Figs. 5,6 and 7. In Fig. 5 I omit the inductance coil ll and connect the platebattery between coils 5. and 10,, as shown rather than to the mid pointof coil 10,... In Fig. 6 the plate battery is shown as connectedto themid point of 10,. This arrangement is similar to that shown in Fig. 5.in Fig. 7, however, I connect the plate battery as in Fig. 5 but in thisinstance I provide a radio frequency choke 18 in the circuit. The objectof connec'ting the plate battery either to the mid point of primarylO ofcoupling coil 10 or providing it with a choke is to prevent anycondenser discharge current from affecting the detector but this is notessential. and as a matter of fact, the arrangen'lent shown in Fig. 5 isentirely satisfactory for the reason that the condenser dischargecurrent is always very small.

It is obvious that I may apply the prim ciple of this invention byshort-circuiting a portion or all of the inductance of the resonantcircuit, or a resistance therein. Of

course, it will be evident that this short cir- .to say, when there isno energy stored in the portion to be short circuited. In the case of aninductance this would be when the condenser is at the point of maximun'icharge. In the case of a resistance, it would be when the oscillatorycurrent is zero.

Having described my invention I declare that what I claim is 1. In radiosignalling apparatus the com bination of a plurality of aerials,indicating means connected to one. only of said aerials, means connectedto another of said aerials for substantially preventing the operation ofsaid indicating means in response to oscillations received on said firstnamed aerial except when the phase difference. between the oscillationsreceived on said aerials has a predetermined value.

2. In radio signallin apparatus the combination of two aerials,indicating means connected to one of said aerials, and means operativelyconnected to the other of said aerials, for preventing the operation ofsaid indicating means in response to signals received upon said firstnamed aerial except when the phase difier'ence between the signals atsaid preventing means has a predetermined value. v

3. In radio signall'n apparatus, the combination of two aerials, anoscillating circuit operatively. associated with one onl of said aerialsand deriving energy there rom and means controlled by the other of said.aerials for preventing oscillations in said circuit, under predeterminedconditions.

4. In radio signalling apparatus, the combination of two aerials, anoscillating circuit operatively associated with one only of said aerialsand deriving energy therefrom, and means controlled by the other of saidaerials for periodically dissipating energy stored in one of the energystoring elements of said circuit.

5. In radio sgnaling apparatus the combination of two aerials, anoscillating circuit operatively associated with one thereof, derivingsignal oscillations therefrom only,

' and comprising a capacity'shunted by an impedance, and meanscontrolled by said other aerial for varying the value of saidimpedance.

6. In radio signalling apparatus the combination of two aerials, anoscillating circuit operatively associated with one only of.

said aerials and deriving energy therefrom, said oscillating circuitcontaining a capacity shunted by a resistance, and means connected tothe other of said aerials for causing the value of said res'stance to becontrolled by oscillations received on. said last named aerial. Y

7. In radio signalling apparatus, thecom bination with an aerial,indicating means, and an oscillating crcuit interposed between saidaerial and said indicating means, of a second aerial havingcharacteristics differing from those of the first aerial and meanscontrolled by oscillations received on sa'd second aerial forsubstantially preventing oscillations in said oscillating circuit whenthe phase relation between the oscillations received on said aerialdifiers from a prede termined value without substantially interferingwith oscillations in said circuit when the'phase relation betweenoscillations receilved on said aerials has su'ch predetermined va ne.

8; In radio signalling apparatus, the combination of a plurality ofaerials, an oscillating circuit operatively associated with one of saidaerials, said oscillating circuit containing a capacity, a vacuum tubehaving its anode'connected to one side of said ca acity, a second vacuumtube having its ano e connected to the other side of said capacity, thecathodes and grids of said tubes being respectively connected togetheranda coupling coil operatively associated with the other of said aerialsconnected across the grids and cathodes of said tubes, substantially asdescribed.

9. The method of reducing interference in the reception of radio signalswhich comprises impressing the received oscillations on an oscillatingcircuit having a capacity,

and periodically discharging-said capacity at a definite time withrespect to the desired signal oscillations.

10. The method of distinguishing between oscillations of the samefrequency but of substantially diife'rent phase, which comprisesimpressing such oscillations on an oscillating circu t having a capacityand tuned to the desired frequency, and periodically short circu'tingsaid capacity only attimes when the energy stored therein by the desiredoscillation is a minimum.

11. The method of reducing interference.

in the reception of radio signals which comprises impressing receivedoscillations on an oscillating circuit tuned to the desiredoscillations, and periodically changing the constants of said circuit ata time when the energy stored in the capacity of said circuit by thedesired signal is a minimum.

12'. The method of receiving radio signals by means of two aerials whichcomprises impressing the signals from one aerial on an oscillatingcircuit and periodically altering at least one of the constants of saidcircuit under control of signals received on the other aerial.

13. The method of receiving radio signals by means of two aerials whichcomprises impressing the signals from one aerial on an oscillatingcircu.t, and .periodically discharging the capacity in said circuitunder the control of signals received on the other aerial 'lation whichconsists in impressing the desired oscillations and the residue ofundesired oscillations upon an oscillating circuit tuned to the desiredosc llation frequency, and periodically discharging an energy storingelement of said circuit at such time with respect to the oscillations ofdesired fre-- quency and phase relation-that the energy stored thereinby such undesired oscillations the desired oscillation frequenc and peissubstantially zero. riodically dissipating axportion o the energy 15. -Amethod of selecting oscillations havstored in one ofthe energy storingelements 10 ing a predetermined frequency and phase reof said circuit ata time when the energy 5 lation which consists in im ressing suchosstored therein by the desired oscillations is cillations plus theresidue 0? undesired oscilsubstantiall zero. x latipns upon anoscillating circuit tuned to RICHKRD HOWLAND RANGER.

